The long-period symbiotic binary CH Cygni III. Emission line profiles from the rotating accretion disk.

We have analysed Hα profiles of the peculiar symbiotic star CH Cygni, obtained in 1982-1986 by the 2 m telescope in Rozhen observatory and by the 1.5 m telescope in Tartu observatory. Theoretical emission line profiles from rotating optically thick accretion disk have been computed and compared with the observations. We have found that Hα profiles of CH Cyg can be considered as arising from a Keplerian disk. Great changes in the line widths are explained as variations of the inner radius of the disk R_in_. Such variations are interpreted in the framework of the magnetic rotator model: in 1981-1984 the star was in the accretor state and R_in_ was about 10 R_sun_; it decreased rapidly down to 0.1 R_sun_ by September 1984, after transition into the propeller state and disruption of the accretion complex around the white dwarf. Afterwards R_in_ again increased up to 8 R_sun_ by April 1986. Changes in the Hα profile show that in 1985 the eclipse of the hot component took place. Hα line observed in August 1985, probably has its origin in bipolar jets ejected in 1984, it cannot be fitted by the rotational profile with reasonable input parameters.